Implantable defibrillators are implanted in patients suffering from potentially lethal arrhythmias. The device monitors cardiac activity and decides whether electrical therapy is required. If a tachycardia is detected, pacing or cardioversion therapy may be used to terminate the arrhythmia. If fibrillation is detected, defibrillation is the only effective therapy.
Both cardioversion and defibrillation require that a high voltage shock be delivered to the heart. Since it is impractical to maintain high voltage continuously ready for use, implantable defibrillators charge up energy storage capacitors prior to delivering a shock to the heart. Currently available defibrillators typically use tubular aluminum electrolytic capacitors as discussed in Troup, "Implantable Cardioverters and Defibrillators" (Current Problems in Cardiology, Volume XIV, Number 12, Dec. 1989, Year Book Medical Publishers, Chicago), and as disclosed in U.S. Pat. No. 4,254,775 entitled "Implantable Defibrillator and Package Therefor", issued in 1981.
Since the capacitors must store approximately 40 joules, their size is relatively large, and it is difficult to package them in a small implantable device. Currently available implantable defibrillators are relatively large (over 10 cubic inches), generally rectangular devices about an inch thick. The patient who has a device implanted may often be bothered by the presence of the large object in his or her abdomen. Furthermore, the generally rectangular shape can in some instances lead to skin erosion at the somewhat curved corners of the device. For the comfort of the patient we have found that it would be desirable to be able to make smaller, and more rounded implantable defibrillators. The size and configuration of the capacitors has been a major stumbling block in achieving this goal.
It is, therefore, an object of the present invention to provide efficient capacitor structure for an implantable cardiac defibrillator.
Another object of the present invention is to provide a capacitor structure which allows the construction of smaller, more physiologically-shaped implantable defibrillators.
Other objects of the present invention will become apparent as the description proceeds.